Without the small, pressurized chamber, a fish's swim bladders likely wouldn't survive the ascent out of water.

Lying in the space 650 to 3,200 feet below the surface of the ocean is the mesopelagic zone. It's here that sunlight begins to fade away, earning it the nickname the “twilight zone.”

This twilight zone is home to critical ecosystems like coral reefs that are home to the diverse fish species that maintain them. It's a depth that humans can't easily access. Remotely operated vehicles (ROVs) and invasive techniques have previously been used to study the complex systems.

But a new invention is helping divers bring fish to the surface, where they can be more easily studied.

A Dangerous Swim

Invented by scientists at the California Academy of Sciences and the Monterey Bay Aquarium, the Submersible Chamber of Ascending Specimens, or SubCAS, is helping bring fish safely to the water's surface. The cylinder is just two feet long and contains just under a handful of fish at a time. A pressurized chamber helps ensure that fish living at intense depths don't sustain internal damage on their journey out of the water.

“Before the SubCAS, hand-collecting and surfacing live fishes involved the invasive process of needling a hole in their gas-filled swim bladders to prevent over-expansion,” says Bart Shepherd, senior director of the academy's Steinhart Aquarium, in a press release.

Most bony fish contain a gas-filled organ called a swim bladder that helps them maneuver through the water without floating to the top or sinking to the bottom.

When twilight zone-level fish are quickly brought to the surface of the water, it can cause that swim bladder to rupture.

The chamber works to correct this rapid change in pressure.

How It Works

When divers reach 180 feet in their ascent, they transfer fish from the jars in which they were collected to a small housing, which they then blow an air bubble into. The chamber is then sealed with the air bubble inside it, and for the remainder of the ascent, the bubble helps maintain greater pressure.

At 100 feet, the fish are then handed off to divers who take them to above-ground facilities, where the fish are released in a controlled decompression.

According to the California Academy of Sciences, the method has been extremely successful. Fish are sometimes transported to different facilities via plane, but the different pressures, from 500 feet below sea to 35,000 feet in the air, has been manageable, say researchers.

Taking a Closer Look

The SubCAS container presents the immediate benefit of helping scientists bring fish to the water's surface, but it also allows them to better study species that are typically out of reach.

For conservationists trying to protect some of these vulnerable species, better understanding how they live can inform more effective conservation strategies.

“In a time of global crisis for coral reefs, discovering strange and beautiful fishes from unexplored reef habitats is critical to our understanding of how to protect them,” says Shepherd in a statement. “These species are ambassadors of important environments that are rarely included in marine protected areas or sanctuaries.”